Dog dander is a common cause of indoor allergy with symptoms including rhinitis, conjunctivitis, bronchial inflammation and asthma. Dog allergens can be detected not only in houses where dogs are kept as pets but also in other places such as schools and day care centres where dogs are not present on a regular basis [1].
Allergy to dog is accompanied and dependent of sensitization to proteins released from dog hairs and dander. In cases of suspected allergy to dog, the clinical investigation includes assessment of sensitization by skin prick or specific IgE antibody measurement using extract of dog hair and/or dander. A laboratory immunoassay for specific IgE, such as a Phadia ImmunoCAP®, can detect most cases of sensitization to dog using natural dog dander extract due to favourable assay conditions and a large solid phase available for allergen attachment.
Dog hair and dander extracts contain a complexity of allergenic and non-allergenic proteins [2, 3]. Four dog allergens have so far been identified and studied in detail: Can f 1, Can f 2, Can f 3 and Can f 5 [4-6]. The former two are both members of the lipocalin protein family and have been purified and expressed as recombinant proteins [4, 7]. Can f 3, dog serum albumin, is a relatively conserved protein showing extensive cross-reactivity to other mammalian albumins [8]. Can f 5, dog prostatic kallikrein, has recently been described as a major dog allergen and shown to cross react with human prostate-specific antigen (PSA) [5]. Of the dog dander allergens known to date, Can f 1 and Can f 5 appear to be most important, binding IgE antibodies from approximately 50% and 70% of dog allergic subjects, respectively [5, 9]. Although about 20-40% of adult dog allergic individuals display IgE antibody binding to Can f 2 or Can f 3, few appear to react exclusively or even dominantly to either of these allergens [5, 9]. In a recently reported study, it was found that a small proportion of dog allergic patients display IgE antibody binding to none of Can f 1, Can f 2, Can f 3 and Can f 5, despite being sensitized to natural dog dander extract [5].
In addition to the allergens discussed above, an IgE-reactive, 18 kDa lipocalin-like protein, distinct from Can f 1 and Can f 2, has been reported and designated Can f 4 [9]. Fifteen of 25 (60%) dog allergic patients were reported to display serum IgE reactivity to this 18 kDa band in immunoblotting, making this a potentially important dog allergen component. However, the allergen has only been characterised as a 13 amino acid N-terminal sequence from an SDS PAGE gel, a sequence yielding no match to any known protein sequence from dog. The full protein sequence is thus unknown, and cloning of a recombinant protein has not been performed. Neither has the native protein been purified, and no suggestion is given as to how cloning of Can f 4 could be accomplished.
In an abstract by Saarelainen et al. published in the Abstract Book of the 3rd International Symposium on Molecular Allergology in Salzburg Apr. 18-20, 2008, it is stated that Can f 4-specific mAb recognized a protein of 20 kDa in cow dander extract.
In a special edition of the scientific journal Allergy publishing the abstracts of the XXVIII Congress of the European Academy of Allergy and Clinical Immunology (EAACI) in Warsaw Jun. 6-10, 2009, there is an abstract disclosing that a cDNA encoding a full-length Can f 4 has been cloned [Allergy 64 (Suppl. 90): 179-538). However no indication is given as to how this cloning could be achieved and no nucleic acid or amino acid sequence is given.